The invention concerns a device to limit the amount of air intake into a rotating mixer operating beneath a liquid surface.
Mixers of this type are used for instance in waste water and in various types of industrial process liquids to maintain a homogeneous mixture and to prevent sedimentation. The mixer is then placed at a distance below the liquid surface directed so that a flow suitable for the mixing vessel is obtained.
The submersible mixer is in common use today. This mixer is comprised of a hydraulic part having a propeller and an attached driving unit. The big advantage with such a mixer is that it is easier to place the mixer advantageously as there is no long shaft connected to a driving unit outside the tank.
When operating in shallow tanks where the mixer must be placed near the liquid surface, specific problems arise. The draw that arises around the mixer means that there is a risk for air intake from the liquid surface. This air intake means a worse efficiency and in addition there is a risk for vibration in the mixer which disturbs the flow and causes mechanical strain in the material. These problems occur mainly if the mixer is situated within or near the liquid surface.
In order to solve the problems it has been suggested to arrange a floating cover on the surface above the mixer.
Such a cover can be useful, but the fact that the liquid level often changes means that the result often is insufficient.
According to the invention, the problem to reduce the risk for air intake to a rotating mixer is solved by the disclosed device.